Information transfer in a multi-mode global positioning system used with wireless networks

ABSTRACT

The present invention discloses a GPS system that can operate in different modes depending on the network facilities and bandwidth available, the GPS information that can be acquired, or user or system requirements. The modes comprise standalone mode, where a mobile communications device computes the position of the device, an autonomous mode, where the mobile communications device transmits the computed position to a server, application, or PSAP in a communications network, a network aided mode, where the network aides the mobile communications device in determining the position of the device, a network based mode, and other modes.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U. S. C. § 119(e) ofU.S. Provisional Patent Application No. 60/225,076, filed Aug. 14, 2000,entitled “MULTI-MODE GLOBAL POSITIONING SYSTEM FOR USE WITH WIRELESSNETWORKS” by Ashutosh Pande, et al., which application is incorporatedby reference herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention.

[0003] The present invention relates in general to Global SatelliteSystem (GSS) receivers, and in particular to multi-mode GlobalPositioning System (GPS) for use with wireless networks.

[0004] 2. Description of the Related Art.

[0005] Cellular telephony, including Personal Communication System (PCS)devices, has become commonplace. The use of such devices to providevoice, data, and other services, such as internet access, has providedmany conveniences to cellular system users. Further, other wirelesscommunications systems, such as two-way paging, trunked radio,Specialized Mobile Radio (SMR) that is used by police, fire, andparamedic departments, have also become essential for mobilecommunications.

[0006] A current thrust in the cellular and PCS arena is the integrationof Global Positioning System (GPS) technology into cellular telephonedevices and other wireless transceivers. For example, U.S. Pat. No.5,874,914, issued to Krasner, which is incorporated by reference herein,describes a method wherein the basestation (also known as the MobileTelephone Switching Office (MTSO)) transmits GPS satellite information,including Doppler information, to a remote unit using a cellular datalink, and computing pseudoranges to the in-view satellites withoutreceiving or using satellite ephemeris information.

[0007] This current interest in integrating GPS with cellular telephonystems from a new Federal Communications Commission (FCC) requirementthat cellular telephones be locatable within 50 feet once an emergencycall, such as a “911” call (also referred to as “Enhanced 911” or“E911”) is placed by a given cellular telephone. Such position dataassists police, paramedics, and other law enforcement and public servicepersonnel, as well as other agencies that may need or have legal rightsto determine the cellular telephone's position. Further, GPS data thatis supplied to the mobile telephone can be used by the mobile telephoneuser for directions, latitude and longitude positions (locations orpositions) of other locations or other mobile telephones that thecellular user is trying to locate, determination of relative location ofthe cellular user to other landmarks, directions for the cellular uservia internet maps or other GPS mapping techniques, etc. Such data can beof use for other than E911 calls, and would be very useful for cellularand PCS subscribers.

[0008] The approach in Krasner, however, is limited by the number ofdata links that can be connected to a GPS-dedicated data supplywarehouse. The system hardware would need to be upgraded to manage theadditional requirements of delivering GPS information to each of thecellular or PCS users that are requesting or requiring GPS data, whichrequirements would be layered on top of the requirements to handle thenormal voice and data traffic being managed and delivered by thewireless system.

[0009] Another patent that concerns assistance between the GPS systemand wireless networks is U.S. Pat. No. 5,365,450, issued to Schuchman,et al. which is incorporated by reference herein. In the Schuchmanreference, ephemeris aiding through the cellular telephone system isrequired for the GPS receiver to acquire and track GPS satellites.However, cellular and other wireless networks do not always have thecapability to provide ephemeris aiding to the mobile GPS receiver.

[0010] It can be seen, then, that there is a need in the art fordelivering GPS data to wireless communications systems, includingcellular and PCS subscribers, in an efficient manner. It can also beseen that there is a need in the art for GPS capable cellular and PCStelephones. It can also be seen that there is a need in the art for GPScapable cellular and PCS telephones that can receive GPS satellite datafor use by the cellular/PCS subscriber. It can also be seen that thereis a need in the art for a large cellular system that can use and/orsupply GPS information to cellular users for a number of applications,including E911 without the requirement of geographically proximatebasestations.

SUMMARY OF THE INVENTION

[0011] To minimize the limitations in the prior art described above, andto minimize other limitations that will become apparent upon reading andunderstanding the present specification, the present invention disclosesa system, device, and method for determining the position of a mobiledevice. The system comprises a geolocation server and a wirelesscommunications device. The geolocation server receives at least onesignal from at least one GPS satellite. The wireless communicationsdevice comprises a GPS receiver section, wherein the GPS receiver can beselectively switched between a standalone mode and at least one othermode for determining a geolocation of the wireless communicationsdevice. The wireless communication device can selectively send thedetermined geolocation of the wireless communication device to thegeolocation server, and the wireless communications device periodicallytransmits a frequency reference message to the GPS receiver.

[0012] It is an object of the present invention to provide a method anda system for delivering GPS data to wireless communications systems,including cellular and PCS subscribers in an efficient manner. It isanother object of the present invention to provide a method and a systemthat can manage GPS capable cellular and PCS telephones. It is anotherobject of the present invention to provide a method and a system for GPScapable cellular and PCS telephones that can receive GPS satellite datafor use by the cellular/PCS subscriber. It is a further object of thepresent invention to provide a method and a system for large cellularsystems to use that can use and/or supply GPS information to cellularusers for a number of applications, including E911.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Referring now to the drawings in which like reference numbersrepresent corresponding parts throughout:

[0014]FIG. 1 illustrates a typical GPS architecture;

[0015]FIG. 2 shows the interface between the call processing section andthe GPS section of the present invention;

[0016]FIG. 3 illustrates another implementation of an end-to-end systemin accordance with the present invention;

[0017]FIG. 4 illustrates a thin server implementation of the presentinvention;

[0018]FIG. 5 illustrates time transfer between the GPS time referenceand the GPS clock in accordance with the present invention;

[0019]FIG. 6 illustrates a frequency transfer block diagram inaccordance with the present invention;

[0020]FIG. 7 illustrates a frequency transfer architecture in accordancewith the present invention; and

[0021]FIG. 8 is a flowchart illustrating the steps used to practice thepresent invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0022] In the following description of the preferred embodiment,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration a specific embodiment inwhich the invention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

[0023] Overview

[0024] When integrating GPS components with wireless communicationssystems (which include cellular, paging, two-way paging, Personal DataAssistant, Bluetooth, and PCS systems), the GPS system must have thecapability to acquire and track the GPS satellites under the conditionsthat the typical wireless communications system user will encounter.Some of those conditions, e.g., indoor use, dense urban areas use thathas a limited sky view, such as in downtown areas with skyscrapersblocking satellite views, etc., although manageable forterrestrial-based wireless communications systems, are difficultsituations for GPS systems. For example, traditional standalone modeGPS, e.g., where the GPS receiver acquires the signals from the GPSsatellites, tracks the satellites, and, if desired, performs navigationwithout any outside information being delivered to the GPS system, hasproblems with long Time To First Fix (TTFF) times, and, further, haslimited ability to acquire the GPS satellite signals under indoor orlimited sky-view conditions. Even with some additional information, TTFFtimes can be over thirty seconds because ephemeris data must be acquiredfrom the GPS system itself, and also requires a strong signal to acquiresuch information reliably. These requirements of the GPS system haveimpacts on the reliability of position availability as well as powerconsumption in handheld wireless communications system devices.

[0025] To overcome these problems, the present invention allows formultiple modes of operation depending on various factors. The GPS systemof the present invention can be used in a standalone mode, for example,when the GPS receiver is receiving a strong signal, has recent ephemerisor almanac data, or when an exact position is not required. However, ifthe GPS system of the present invention is not receiving a strong enoughGPS signal e.g., the handheld wireless communication device is beingused indoors, the GPS system of the present invention can switch to adifferent mode of operation, e.g., a mode of operation where thewireless communication system helps or “aids” the GPS system to acquire,track, and/or navigate using the GPS signals received by the GPSreceiver and additional information supplied by the wirelesscommunications system. This mode of operation is called a “networkaided” mode. Further still, the GPS system of the present invention,when being used in an even harsher signal reception environment, can becompletely dependent on the wireless communications system to provideposition information to the GPS receiver or mobile handset, and the GPSsystem of the present invention would then operate in a wirelesscommunications network provided or “network based” mode of operation.The GPS system of the present invention can switch between these modesof operation based on several variables, as well as user-selectedpreferences or demands, and can switch either via local or remotecontrol, or via either automatic or manual commands given to the GPSsystem.

[0026] In addition, the multi-mode operation of the present inventionallows for additional benefits to accrue to the integrated GPS/wirelesscommunications system as described herein.

[0027] GPS Architecture

[0028]FIG. 1 illustrates a typical GPS architecture.

[0029] The wireless handset location technology of the present inventionuses GPS technology in support of various wireless handset devices forthe implementation of E911 and geo-location services. By taking theadvantage of the low cost, low power, high performance and high accuracyGPS receivers enabled by the present invention, as well as the wirelessnetwork communication services, the wireless handset location technologyof the present invention provides highly reliable and economicalsolutions to the Wireless Aided GPS.

[0030] The wireless handset location technology of the present inventionsupports all kinds of geo-location services, from fully standalone mode,network aided mode, to network based service mode, to other modes. Thetechnology of the present invention also accommodates wide range ofwireless communication platforms, including CDMA, TDMA, AMP, and evenpager systems. FIG. 1 portrays the concept of wireless handset locationtechnology.

[0031] System 100 illustrates a GPS satellite 102, which is illustrativeof the constellation of GPS satellites 102 that are in orbit, a wirelesshandset 104 that comprises a GPS receiver, a base station 106, ageolocation (server) service center 108, a geolocation end application110, and a Public Safety Answering Point (PSAP) 112.

[0032] The GPS satellite 102 transmits spread spectrum signals 114 thatare received at the wireless handset 104 and the geolocation server 108.For ease of illustrative purposes, the other GPS satellites 102 are notshown, however, other GPS satellites 102 also are transmitting signals114 that are received by the wireless handset 104 and the geolocationserver 108. If the wireless handset 104 can receive a strong enoughsignals 114, the GPS receiver in the wireless handset 104 can computethe position of the wireless handset 114 as is typically done in the GPSsystem. However, wireless handsets are typically not able to receivestrong enough signals 114, or are not able to receive signals fromenough GPS satellites 102 to autonomously compute the position of thewireless handset 104, but can still communicate with base station 106.Thus, base station 106 can communicate information via signals 116 tohandset 104 to allow handset 104 to compute the location, or cancommunicate information from handset 104 to the geolocation server 108to allow the geolocation server 108 to compute the position of thehandset 104. If the basestation 106 is transferring information to thehandset 104 to allow the handset 104 to compute position, it is called“wireless-aided GPS,” whereas when the basestation 106 transfersinformation from the handset 104 to the geolocation server 108 for thegeolocation server 108 to compute the position of the handset 104 it iscalled “network-centric GPS.”

[0033] Geolocation server also communicates with geolocation application110 via signals 118 and with PSAP 112 via signals 120. These signals 118and 120 can either be via wireless links or can be through the land linetelephone network or other wire-based networks.

[0034] The wireless handset 104 location technology of the presentinvention comprises two major service systems: the wireless handset 104with the GPS receiver of the present invention and the geo-locationserver 108 containing the geo-location software modules of the presentinvention. In addition, there are two types of supporting systems: theBase Station (BS) 106 infrastructure, which provides the networkinformation transfer mechanism, and the PSAP 112 or the application 110system, which can initiate the geo-location network services.

[0035] The handset 104 comprises a typical wireless handset 104 sectionthat performs the call-processing (CP) function, and a GPS section forposition computation, pseudorange measurement, and other GPS functionsperformed at the handset 104 of the present invention. A serialcommunication link, or other communications link, performs thecommunications between the CP section and the GPS section. A collectionof hardware lines is utilized to transmit signals between the CP and GPSsection.

[0036]FIG. 2 shows a typical interface between the Call Processingsection and the GPS section of the present invention.

[0037] As shown in FIG. 2, handset 104 comprises a Call Processing (CP)section 200 and a Global Positioning System (GPS) section 202. Withinhandset 104, or, alternatively, between handset 104 and an externalaccessory to handset 104, communications between CP section 200 and GPSsection 202 take place. These communications allow signals to betransferred from CP section 200 to GPS section 202, and typically takeplace on a serial communications link 204 and hardware lines 206, butother connections can be used if desired.

[0038] For example, in another implementation, the CP section 200 andthe GPS section 202 can share the same digital processor and othercircuitry. In such a case, the communication between sections can bemade by inter-task communication, and certain data transfers, such asany time or frequency transfers between the CP section 200 and the GPSsection 202, would not use hardware lines 206, but would be internal tothe circuitry or, potentially, no transfer would be required dependingon the circuit design.

[0039]FIG. 3 illustrates another implementation of an end-to-end systemof the present invention.

[0040] System 300 shows signals 114 that are received at handset 104,which comprises a GPS receiver client 302 and a CP section 304,connected by, typically, an RS232 data link 306. The CP sectioncommunicates with base station 106, which communicates with a mainserver 308 via the cellular and/or cellular/land-based telephonenetwork. The main server 308 communicates with the geolocation server108 and the application 110 via land-based or wireless networks,typically using TCP/IP protocols.

[0041] The GPS signals 114 are also received by a series of referencereceivers 310 which compute the position of the reference receivers andextract data from the GPS signals 114. The extracted data, e.g., time,Doppler, frequency, etc. is sent to a GPS data center 312, for all ofthe satellites in the GPS constellation 102. When needed, thegeolocation server 108 extracts data from the data center 312 for use bythe handset 104, and transmits the needed or requested data from thehandset 104 or the application 110. The main server can also interfaceto the PSAP 112 if desired, and the main server 308 and the geolocationserver 108 can be co-located if desired or necessary.

[0042] Depending on the wireless network being used, e.g., cellular,PCS, two-way paging, Specialized Mobile Radio (SMR), Short MessagingService (SMS), etc. the physical implementation of the present inventionmay vary from that shown in the figures. The figures are used forillustrative purposes only, and are not meant to limit the applicationof the present invention to other wireless systems. Further, the presentinvention can be used with hardwired systems, e.g., the landlinetelephone system, local area networks, etc., without departing from thescope of the present invention.

[0043]FIG. 4 illustrates another embodiment of the present invention.

[0044] System 400 illustrates GPS constellation 102 transmitting signals114 that are received by handset 104. Handset 104 comprises GPS receiver402, also called the client 402, a server 404, and a CP section 406. Insystem 400, server 404 is known as a “thin server,” since it will nothave the same capabilities of server 108 described in FIG. 3. System 400uses GPS reference receiver 310 to also receive signals 114 from GPSconstellation 102, and stores the GPS data in data center 312. Thisinformation is transmitted to main server 308 when requested byapplication 110, or by handset 104, which uses server 404 to transmitthe data back and forth between the CP section 406 and client 402.System 400 allows for some aiding data, e.g., ephemeris, to be stored inthe cellular handset at the server 404, and then provided to the GPSclient 402 on demand.

[0045] Multi-Mode GPS Operation with Wireless Networks

[0046] As described above, the system of the present invention can beoperated in different modes depending on a number of variables, e.g.,signal strength, operator intervention, type of services desired orrequested, performance expectation, e.g., TTFF of a few seconds vs. tensof seconds, etc. The operation of each mode is described herein below.

[0047] Standalone Mode

[0048] In standalone mode, the GPS receiver 202 located in the mobilecommunications device (also known as a handset 104 or PDA) operatesindependently from the wireless communications network. The GPS receiver202 acquires GPS satellite 102 signals 114, and uses those signals 114to determine the location of the GPS receiver 202. The GPS receiver 202also uses GPS satellite 102 signals 114 for tracking, and, if desired,navigation functions. The determined position is used internally to themobile communications device 104.

[0049] Autonomous Mode

[0050] In autonomous mode, the position of the handset 104 is computedin a similar manner as in Standalone Mode, e.g., by the GPS receiver 202in handset 104 without any assistance from the cellular or othercommunications network. However, instead of using the determinedposition internally to the handset 104, in autonomous mode, the handset104 transmits the determined position of the handset 104 back to thecommunications network, e.g., to the geolocation server 108, toapplication 110, to PSAP 112, etc., through the wireless communicationsnetwork.

[0051] Network-Aided Mode

[0052] A different mode of operation can be implemented such that theGPS receiver uses the wireless communications network to deliver some ofthe position information to the GPS receiver to “aid” the GPS receiverin the acquisition, tracking, and navigation functions. Such informationcomprises almanac or sub-almanac information, coarse positioninformation, Doppler data, in-view satellite positions, time andfrequency aid, received wireless radio signal strength (to obtain byanalogy an idea of what to expect for the GPS signal strength), or otheraids that will aid the GPS receiver in acquiring the information thatthe GPS receiver needs to acquire, navigate, or track. Such situationscan occur when the GPS receiver has a limited view of the sky, or cannotacquire enough GPS signals on it's own, because the GPS receiver isblocked or otherwise unable to acquire the GPS satellite signals, orcannot track the satellites because of multipath problems. Further, suchsituations may also be desired by the user conditioned upon a givenevent, e.g., an E911 call is placed from the mobile handset, the userwants a very short TTFF, the user may desire additional networkinformation to be included in the GPS calculation for increasedaccuracy, or other reasons.

[0053] The Network Aided approach differs from the Network Centric (Alsocalled the Network Assisted mode in other literature) approach becausein the Network Aided approach, the GPS receiver could, eventually,obtain the position and tracking information needed to locate the GPSreceiver by itself. The Network Centric approach, as discussed inKrasner, cannot determine the position of the mobile receiver solelyusing the GPS information acquired from outside the wireless network,because the position calculation is done inside of the wireless networkat the basestation, instead of in the mobile communications device asdescribed in the present invention.

[0054] Further, the Network Aided approach, as described with respect tothe present invention, allows for switching between standalone mode,autonomous mode, or other modes, once the initial acquisition has beenmade. The Network Aided mode and architecture of the present inventionallows for the tracking, e.g., continuous update of user position to bedone in Autonomous mode or standalone mode even in weak signalenvironments. The Network Assisted architecture of Krasner typicallycontinues to depend on the network aid to calculate subsequent position.

[0055] The Network Aided mode is typically only used for acquisition ofthe GPS signal in weak signal environments. Once the GPS signal isacquired, the GPS receiver of the present invention can track the GPSsignal without aid from the network. The Network Assisted mode ofKrasner requires the network to assist the GPS receiver for trackingpurposes as well as for acquisition.

[0056] Network Based Mode

[0057] A network based mode can also be used for situations when the GPSreceiver cannot receive any GPS signals. As such, the GPS system iscompletely dependent on the wireless communications network to obtainany positioning information, and as such, is “centered” upon theinformation delivered by the wireless communications network. Typically,network-based modes compute position without using GPS or othersatellite information. Positions of handsets 104 are derived fromnetwork resources, e.g., cellular transmitter towers and Time DifferenceOf Arrival (TDOA) techniques. When a handset 104 is in an area where itcannot receive GPS or other positioning system information to determinehandset 104 position, such a mode can be useful.

[0058] Other Modes

[0059] The system of the present invention can, in Standalone,Autonomous, Network Aided, or Network Based modes, can also receiveinformation from outside the wireless communications network as well asoutside of the GPS satellite system. For example, in Autonomous mode orStandalone Mode, the GPS receiver can receive information from the GPSsatellites and a Bluetooth network, while using the cellular wirelessnetwork to transmit voice or data. The GPS acquisition, tracking, andnavigation functions can be enhanced with inputs from the Bluetoothnetwork without using the cellular network. Similar scenarios can alsobe envisioned within the scope of the present invention that occurwithin the Network Aided or Network Based modes. Further, the presentinvention can operate in a Reverse Aiding (RA) mode which sends GPSinformation back to the wireless communications network for use withinthe wireless communications network

[0060] Further, the architecture and system of the present invention canbe extended to wired networks such as the telephone network withoutdeparting from the scope of the present invention. For example, if GPScapabilities are present in a laptop or PDA and the device is connectedto a wired or wireless Internet link, the GPS calculations can be aidedvia the Internet to calculate a position inside a building. The positioncan be displayed locally or sent to a server. Such a system can be usedfor security or other telephone or hardwired system applications.

[0061] The present invention can also be used for wireless Networkmonitoring, where the position information, alongside with the wirelesssignal strength, or any position-related information, can be collectedfrom every user requesting assistance, at a central place in thenetwork, to continuously monitor the cell coverage area, the amount oftraffic within a single cell, where the traffic is concentrated, whatare the areas of bad wireless reception, to help in the decisions ofadding new base stations, or relocating them. The quality of service canbe monitored in real-time by all the mobile systems used in the area.

[0062] Comparison of the Operation Modes

[0063] The operation modes of the present invention allow furtherflexibility within the GPS receiver framework. When the GPS receiver isnot constrained by short TTFF requirements, or by network bandwidth, orby other signal demands, the GPS receiver of the present invention canbe programmed to automatically select a given acquisition mode. Forexample, when the network traffic is heavy, which translates to a smallbandwidth availability in the wireless communications network, thepresent invention allows the user to automatically or manually selectthe autonomous mode or standalone mode, which is not dependent on thewireless communications network for aiding information. In the same way,when the geolocation server 108 usage is heavy, and the aidinginformation latency time is incompatible with the requirements, the usercan select, either automatically or manually, the autonomous orstandalone mode. However, if additional bandwidth in the wirelessnetwork is available, or if the user needs a short TTFF for an E911call, the present invention allows for manual or automatic override ofthe autonomous or standalone mode of operation into either autonomous orstandalone (if ephemeris is current and there is implicit aidinginformation), the Network Based or network aided modes. Further, if thenetwork is unable to deliver the reliability required, or the networkdoes not have aiding capabilities, the GPS can use other modes or othersources of information to augment the autonomous or standalone mode, inan operational mode called “Augmented Autonomous Mode (AAM).” AAM can beused with Bluetooth, or other sensors such as pressure, accelerometers,or gyros to provide the GPS with aids outside of the network being usedfor communications. For example the present invention can use Bluetoothtransmitters in every floor of a high rise sending its location andfloor information to the phone and this ‘augmented information’ will besent in case GPS cannot be acquired inside the building to deliverpositioning data. Further, the present invention allows for the wirelesscommunications device to switch from standalone mode to another mode,e.g., aided mode, network centric mode, etc., when a predetermined eventoccurs. Such a predetermined event may be the lapse of a predeterminedamount of time without acquisition of a GPS satellite signal, apredetermined number of seconds or minutes, etc., where the wirelesscommunications device is unable to receive any GPS signals, powercycling of the device, etc.

[0064] The multimode architecture of the present invention allows for anautomatic seamless and reliable response, by taking advantage of thenetwork assists if and when available, and allows the system to operateindependently if the assistance is not available or not available in atimely manner. The Network aided operational mode overcomes the start-uplimitations of the autonomous or standalone GPS and allows same level ofperformance as the Network Based mode, but does not require continuousnetwork connectivity after start-up. If the aiding data (ephemeris,approximate location, approximate time etc.) has been received by thecellular phone over some communication medium, the communication linkcould be off when the GPS is started. This is the store and forwardmethod of having a thin server directly mounted on the wirelesscommunications device. The seamless nature and flexibility of thearchitecture enables service providers to tune the system to meet theirneeds based on the capabilities of the network and the type of servicesdesired.

[0065] Further, the selection of the operational mode can depend on thetype of service or the accuracy that the user has requested or demandedfrom the system. For example, if the user places an E911 call, the GPSreceiver can automatically be placed in the mode that will provide themost accurate position information in the most timely manner possible.That mode may be Network Based, but, if the network cannot supply acomplete GPS information set such that the mobile GPS receiver candetermine position calculation information, the receiver can switch toNetwork Aided, such that the processing capabilities of the network andthe GPS receiver are being used in parallel. As another example, if auser is requesting directions to a specific location, the receiver canautomatically select autonomous or standalone mode which will provideinformation in a timely manner, but not place such demands on the powersupply and processing capabilities of the system. Further, the presentinvention allows the user to override the automatic choice ofoperational mode. The system can also switch between modes once apredetermined event, e.g., the first position calculation of the GPSreceiver, is obtained. For example, if an E911 call is placed, thepresent invention may select Network Aided mode to get the positioninformation to the handset as fast as possible. Once that information isdelivered, and the first position is calculated, the present inventionmay switch to a different mode, such as autonomous mode or standalonemode to make additional bandwidth in the wireless communications networkavailable to other users. The architecture of the present invention alsoallows for reception of aiding information and gives the user the choiceto accept that the position be sent back to the network, or “locked” inthe mobile system, available only to the user, if the user wants it forprivacy reasons.

[0066] The architecture of the present invention also gives the user thechoice of preventing the network connection for assistance, even whenthe GPS receiver has determined it is necessary to reach the user'srequirements, in the case the network access is charged to the user on aper use basis. In such a circumstance, the GPS receiver will attempt toprovide a position in standalone mode, but with no guarantee aboutfulfilling the original user's requirements. The present invention thusallows for the bandwidth of the wireless communications network to bemanaged such that the bandwidth can be used more efficiently. Further,the present invention allows for dynamic allocation of the networkresources, including the processing available on the GPS receiver, toprocess as much information in parallel as possible. This allows fordynamic loading of the GPS client and network server processors to moreefficiently calculate position for multiple users. This approach allowsfor an increased number of wireless communications system users withoutsignificantly affecting the infrastructure of the wirelesscommunications system.

[0067] Multi Correlator Architecture

[0068] To assist the system of the present invention, multiplecorrelators can be used to provide the system with a shorter TTFF, amore accurate position, or a more reliable result with fewer transfersfrom Autonomous or Standalone Mode to the Network Aided mode or NetworkBased mode.

[0069] Distributed Smart Client/Server Architecture

[0070] By allowing the GPS receiver (also known as the client) and thewireless communications system (also called the server) to distributethe workload of acquisition, tracking, and navigation tasks in anintelligent manner, the present invention allows for faster acquisition,faster TTFF times, and allows parts of the GPS receiver system to bepowered down or selectively powered to reduce power consumption of theGPS portion of the mobile device.

[0071] The architecture of the present invention also allows for advancequalification of ephemeris data, e.g., validation of stored ephemerisdata quality, by using the network aided mode to verify that the storedephemeris data at the GPS receiver is still valid. Similarly, theNetwork Aided mode allows the present invention to derive coarselocation data to be used for a Coarse Location Acquisition scenario,where a timetag approximate position based on known ephemeris oralmanacs and post processing of the data is used for actual locationdetermination.

[0072] The Other (Augmented Autonomous) Mode also allows for the use oflow power short range wireless technology, such as Bluetooth, to aid theGPS receiver in reducing Time To First Fix (TTFF) times, as well asusing low power short range wireless technology to aid GPS receiver withapproximate location.

[0073] The present invention also allows correction information to besent to the GPS system via the wireless communications network, byswitching between the Autonomous or Standalone and Network Aided modes,or by remaining in the Network Aided mode, for slow changing errors toobtain precise local position, e.g., Iono correction factors, newsub-almanac information, etc. The present invention also can allow fordata “fusion” from various sources, e.g., accelerometer, pressuresensors, tilt meters, etc. also present on the wireless communicationsdevice to add to the accuracy of the position determination, as well asproviding the wireless communications device with approximate location,time, and frequency information to assist the wireless communicationsdevice in determination of a more precise position determination and/orimprove the TTFF time for each client.

[0074] Reverse Aiding

[0075] The present invention also comprises an apparatus for sharing acommon frequency reference between a location determination device and awireless communication equipment, which can Reverse Aid (RA) thewireless communications system to steer or direct transmission beams tothe wireless handset. This will allow additional frequency reuse or codereuse within a cell, since the wireless communications system can nowused phased array technology to beam steer or beam form a shapedtransmission beam that is centered upon each mobile user. This allowsfor lower transmitter power to be used from the basestation transmitter,as well as lower power from the mobile user, because the formed orsteered beam typically has more gain than an omnidirectional beampattern. This feature of the present invention helps to optimize thecommunications links and increase the capacity of wirelesscommunications system basestations, which, in Code Division MultipleAccess (CDMA) networks is very useful since the capacity of CDMAnetworks are limited by the noise floor increase as more users areplaced on the network, not by the code efficiency.

[0076] RA can also be used for accelerating the acquisition and codesynchronization onto the wireless network by providing very accurateabsolute time and frequency references. RA can also be used to help todetermine when to switch to another base station by using the GPSposition (GPS-aided base station hand-over).

[0077] RA can also be used from mobile to mobile, using the network onlyas communication medium, where a first mobile system gets an absolutetime information, measures the difference between network time and GPStime, and sends back the information to the network. The next userrequesting GPS aiding information will receive the GPS time versusnetwork time difference, and will correct the network time of thisinformation to get GPS time to help in its own GPS acquisition process.

[0078] In another embodiment, the network, receiving redundant timeand/or frequency reference information from several users in the samearea for different points in time, can model the network time offset andfrequency drift, and predict its value in the future. This way, thenetwork can provide timing assistace information to a new mobile, evenafter a period where no information is received from any mobile.

[0079] RA from user to user also applies to frequency transfer, wherethe frequency error measured between network frequency and GPS frequencyin a mobile is sent back to the network, and sent back to a new user aspart of the assistance information

[0080] Direct GPS aiding from mobile to mobile without using the servercan also be used without intervention of a server momentarily storingassistance information before retransmitting to the next user requiringaiding. A mobile having acquired a position, having valid ephemeris andpossibly network time and frequency error versus GPS, can broadcast thisinformation to any other mobile in the same vicinity via thebasestation.

[0081] RA can also be used to correct multipath problems at the client,because the terrestrial based wireless communications network can assistin the modeling of the multipath and/or provide modeling tools to helpcorrect the multipath reception problems at the client given theposition of the client.

[0082] Further, the present invention allows RA to use velocityinformation from a GPS receiver to assist the wireless communicationsystem in aligning the Phase Locked Loop (PLL) to address problemsassociated with user motion. In particular, it can increase theeffective wireless cell radius by guiding the wireless tracking loopsusing the absolute user velocity information from GPS, and thus allowwireless operation at lower radio signal strengths.

[0083] Time and Frequency Aiding

[0084] Wireless network systems typically have high quality referenceclocks, and some wireless network systems, such as CDMA, aresynchronized on absolute GPS time. The present invention allows for thewireless network frequency reference to be transferred to the GPSsection of the handset to estimate GPS clock frequency offset andsignificantly reduce the frequency uncertainty. The GPS time referencecan also be transferred to the GPS section to the GPS clock time. Themain purpose of time and frequency transfer is to reduce theuncertainties of receiver clock time and frequency, thus, to improve theTTFF. The time transfer can also contribute to improve the sensitivity.

[0085] Time Transfer

[0086]FIG. 5 illustrates a time transfer mechanism as used inconjunction with the present invention.

[0087] System 500 illustrates a typical wireless network systemssynchronized on absolute GPS time, such as CDMA or GSM with LocationMeasurement Units (LMU). Typically, the GPS time reference 502 istransferred to the GPS section of the handset 104 to synchronize GPSclock time with GPS time. For the wireless handset location system ofthe present invention, the time transfer can be accomplished in threesteps.

[0088] In the first step, the Base Station (BS) clock 504 can besynchronized to the GPS time reference 502. The time accuracy at the BSclock 504 depends on the system configuration and can be in the range of100 to 300 nanoseconds. This is a built-in feature of certain types ofnetworks.

[0089] In the second step, the CP clock 506 is synchronized onto the BSclock 504 by timing the reception of one specific event in the masterframe transmitted from the BS clock 504 to the CP clock 506. The BSclock 504 transmits the master frame with the transmission time of thefirst bit predictable in absolute GPS time with an accuracy of 300nanoseconds. The synchronization error between the BS clock 504 and theCP clock 506 is caused by the RF reference point in the BS clock 504signal, group delay in the BS clock 504, signal transmission time due tothe distance between the handset 104 and the base station, the groupdelay in the CP section, and the handset 104 architecture.

[0090] As long as the handset 104 tracks the base station, the CPsection of the handset 104 knows the absolute GPS time and can predictthe associated accuracy of the GPS time at the handset 104, measured andadjusted during product integration phase, not in real time. If thehandset 104 loses track of the base station or the BS clock 504, the CPclock 506 accuracy will degrade. The CP clock 506 performancedegradation can be predicted based on the CP clock 506 frequencystability, which is normally represented by the Allan variance, and theage of the last tracking.

[0091] The wireless handset location system of the present invention isdesigned to be air-interface independent As the handset 104 manufacturerhas the knowledge of tracking conditions, the CP clock 504 frequencystability, and the air-interface performance, the handset 104manufacturer can determine the preferred or best method to providemodels and/or interfaces to the GPS clock 508 to transfer the absoluteGPS time and the associated accuracy including all uncertainty effects.

[0092] In the third step, the GPS dock 508 asks the CP section clock 506for a time transfer message via the communications link between the GPSsection and the CP section. Typically, this time transfer requestmessage contains no parameter.

[0093] The CP section 200 can react to such a message in severaldifferent ways. The CP section can generate a precise timing event andreturn a time transfer response message. The timing event is typically asingle rectangular pulse, with either a rising edge active or fallingedge active. The time transfer response message typically contains thetime of the timing event in GPS week, seconds into the week, and timeuncertainty in seconds. By timing the timing event using the GPS clock508, the GPS clock 508 is synchronized onto CP clock 506 time.

[0094] The CP section 200 can also send a “delta” message back to theGPS section. For example, the CP section 200 or GPS section 202 canmonitor the CP clock 506 and GPS clock 508. When a time transfer requestis made, the CP section 200, or the GPS section 202, whichever sectionis monitoring the clocks, receives a GPS time 502, a differencecalculation is made between the GPS clock 508 and the GPS time 502. Thisdelta can then be used for GPS calculations and position determinationsuntil a new time transfer is requested.

[0095] The timing information is typically required when the GPS section202 begins a new search on a new GPS satellite 102. The timingsynchronization can be made only periodically at the request of the GPSsection 202. The effective time accuracy available for the search willbe degraded over time since the last reference time and/or frequency wassent due to the quality of the GPS dock 508; however, the approachdescribed with respect to the present invention reduces or eliminatesthe need for locking the GPS clock 508 to the CP clock 506, as well ashaving the CP clock 506 locked to the GPS time reference 502 via the BSclock 504. The frequency stability of the GPS clock 508 represented byits Allan variance as well as the frequency stability over temperaturewill be utilized to predict the time uncertainty at the beginning of theGPS satellite 102 signal search. The present invention aides the handset104 in correctly predicting the time degradation effects, to choose thetime transfer periodicity, and to implement the time transfer since thecontrol of the GPS clock 508 choice and when the next search is made isunder the control of the system of the present invention.

[0096] Frequency Transfer

[0097]FIG. 6 illustrates frequency transfer as used in conjunction withthe present invention.

[0098] Within a cellular telephone system, such as the CDMA system usedin the United States, each Base Station (BS) 106 has a high qualityreference clock. System 600 shows that the BS clock 600, with anassociated BS clock 600 frequency, can be transferred to the CP clock602 and then to the GPS clock 604 as follows, to estimate the GPS clock604 frequency offset as necessary.

[0099] Typically, the CP section 200 tracks the wireless network signalsand measures the CP clock 604 frequency offset relative to the BS clock602. The CP clock 604 frequency uncertainty after this measurement iscaused by BS clock 602 frequency offset, which is specified by thenetwork standards, handset 104 tracking loop performance, CP clock 604frequency stability, and handset 104 motion.

[0100] The CP section 200 then periodically transmits a frequencyreference message to the GPS section 202. This message typicallycontains the error in frequency between the CP clock 604 and the BSclock 602. The frequency reference message is sent at a perioddetermined by the handset capabilities, as well as the necessity of theupdates based on the GPS clock 606 and/or CP clock 604 requirements. Forexample, if the GPS clock 606 and CP clock 604 are both high qualitycrystals, the update message may be sent less often than if the GPSclock and the CP clock are both low quality crystals, or in some casesonly once. However, the periodicity of the frequency error update isselectable by the handset 104 manufacturer. Because the GPS clock 606 iscompared to the CP clock 604 at its own rate as described below, any CPdock 604 vs. BS clock 602 drift between frequency reference messageswill be added to the uncertainty of the GPS clock 606. Another methodfor setting the CP clock 604 is to steer the CP clock 604 onto thereceived signals and synchronized onto BS clock 602, which alleviatesthe need for a frequency reference message.

[0101] Other approaches, such as U.S. Pat. No. 5,841,396, issued toKrasner, which is incorporated by reference herein, describe aphase-locked loop approach to locking the GPS clock 606 to the CP clock604. The present invention avoids the additional circuitry and signaltransfer between the CP section 200 and the GPS section 204 that iscontemplated by such an approach, which makes the present inventioneasier and less expensive to implement in an existing cellular,wireless, or wired telephone system.

[0102]FIG. 7 illustrates the frequency transfer architecture used inconjunction with the present invention.

[0103] System 700 shows a system that can maintain the overall frequencyerror within limits imposed by the total frequency error budget withoutlocking the GPS clock 606 to the CP clock 604. Handset 104 manufacturerscan design specific bounds of the message periodicity depending on theresidual budgeted frequency error after adjusting the frequency and/ortime using the reference message, and Allan variance characteristics ofthe CP clock 604. The transmitted information is the relative frequencyerror, not the absolute error (in Hz), because the GPS section 202 doesnot know the absolute frequency of the CP clock 604. The message thatthe GPS section 202 needs is independent from the nominal CP clock 604frequency.

[0104] The GPS section 202, and the GPS clock 606, use the uncertaintyinformation of the CP clock 604 frequency to optimize signal acquisitionperformance. Everything in the error budget, other than the handset 104motion, depends on the wireless infrastructure and the CP section 200architecture. The CP section 200 sends the GPS section 202 messagesperiodically, which messages contain CP clock 604 nominal frequency inHz, e.g., the frequency of the divided CP clock 604 is sent to thecounter 702 by the CP section 604 for measurement to convert absolutefrequency error into a relative frequency error, CP clock 604 relativefrequency offset vs. BS clock 602 frequency, and CP clock 604 frequencyoffset uncertainty.

[0105] The GPS section 202 then measures the relative frequency betweenthe GPS clock 606 and the CP clock 604 using a counter 702. Theeffective width of the counter gating signal is determined by counting apredetermined number of GPS clock 606 pulses. The number of CP clock 604pulses during this gating signal is used to determine the relativefrequency error between the GPS clock 606 and the CP clock 604.

[0106] The frequency drift between transmission of the frequencyreference information depends on the Allan variance of the GPS clock 606and its stability over temperature. The periodicity of sending of thefrequency reference information can be adjusted depending on maximumfrequency error allocated to the GPS clock 606, and quality of the GPSclock 606. In an alternate embodiment, or for convenience ofimplementation, a frequency divider can be inserted between CP clock 604and Counter 702, thus reducing the absolute frequency to be measured bythe counter.

[0107] Process Chart

[0108]FIG. 8 is a flowchart illustrating the steps used to practice thepresent invention.

[0109] Block 800 illustrates receiving at least one signal from at leastone GPS satellite at the mobile device, wherein the mobile device can beselectively switched between a standalone mode and at least one othermode.

[0110] Block 802 illustrates periodically transmitting a frequencyreference message to the device.

[0111] Block 804 illustrates determining the geolocation of the deviceusing the at least one signal and the frequency reference message.

[0112] Conclusion

[0113] This concludes the description of the preferred embodiment of theinvention. The following paragraphs describe some alternative methods ofaccomplishing the same objects. The present invention, althoughdescribed with respect to GPS systems, can be utilized with anySatellite Positioning System (SATPS) without departing from the scope ofthe present invention. Further, although described with respect to acellular telephone system, other wireless or wire-based systems can beused in place of or in conjunction with the cellular system hereindescribed without departing from the scope of the present invention.Other methods of frequency transfer and time transfer can be utilizedwithout departing from the scope of the present invention.

[0114] In summary, the present invention discloses a system, device, andmethod for determining the position of a mobile device. The systemcomprises a geolocation server and a wireless communications device. Thegeolocation server receives at least one signal from at least one GPSsatellite. The wireless communications device comprises a GPS receiversection, wherein the GPS receiver can be selectively switched between anautonomous mode or standalone mode and at least one other mode fordetermining a geolocation of the wireless communications device. Thewireless communication device can selectively send the determinedgeolocation of the wireless communication device to the geolocationserver, and the wireless communications device periodically transmits afrequency reference message to the GPS receiver.

[0115] The foregoing description of the preferred embodiment of theinvention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. It is intendedthat the scope of the invention not be limited by this detaileddescription, but rather by the claims appended hereto.

What is claimed is:
 1. A geolocation system, comprising: a geolocationserver, wherein the geolocation server receives at least one signal fromat least one GPS satellite; and a wireless communications device,comprising a GPS receiver section, the GPS receiver being selectivelyswitchable between a standalone mode and at least one other mode fordetermining a geolocation of the wireless communications device, and thewireless communication device can selectively send the determinedgeolocation of the wireless communication device to the geolocationserver, wherein the wireless communications device periodicallytransmits a frequency reference message to the GPS receiver.
 2. Thegeolocation system of claim 1, wherein the at least one other mode isselected from a group comprising an autonomous mode, a network aidedmode, a network centric mode, and a reverse aiding mode.
 3. Thegeolocation system of claim 2, wherein the frequency reference messagecomprises an error in frequency between a call processing clock and abase station clock.
 4. The geolocation system of claim 3, wherein a GPSclock in the GPS receiver is periodically compared to the callprocessing clock to determine a frequency offset of the GPS clock. 5.The geolocation system of claim 4, wherein the periodic transmission ofthe frequency reference message and the periodic comparison of the GPSclock to the call processing clock have the same period.
 6. Thegeolocation system of claim 5, wherein the GPS receiver switches betweenthe standalone mode and the at least one other mode when a predeterminedevent occurs.
 7. The geolocation system of claim 6, wherein thepredetermined event is initial acquisition of at least one GPS satellitesign.
 8. The geolocation system of claim 7, wherein the selectiveswitching of the GPS receiver switches the receiver from the at leastone other mode to standalone mode.
 9. The geolocation system of claim 6,wherein the selective switching of the GPS receiver switches thereceiver from standalone mode to the at least one other mode.
 10. Thegeolocation system of claim 9, wherein the predetermined event is alapse of a predetermined amount of time without acquiring at least oneGPS satellite signal.
 11. The geolocation system of claim 6, wherein thewireless communications device can receive information from a secondsource, the second source selected from a group comprising a bluetoothnetwork, a Specialized Mobile Radio network, a Personal CommunicationSystem (PCS) network, a wireless Local Area Network, an infrarednetwork, a paging network, a two-way paging network, and an FM broadcastnetwork.
 12. The geolocation system of claim 2, wherein the frequencyreference message steers the call processing clock onto the base stationclock, and the frequency reference message is only sent once to thewireless communications device.
 13. The geolocation system of clam 12,wherein a GPS clock in the GPS receiver is periodically compared to thecall processing clock to determine a frequency offset of the GPS clock.14. The geolocation system of claim 13, wherein the GPS receiverswitches between the standalone mode and the at least one other modewhen a predetermined event occurs.
 15. The geolocation system of claim14, wherein the predetermined event is initial acquisition of at leastone GPS satellite signal.
 16. The geolocation system of claim 15,wherein the selective switching of the GPS receiver switches thereceiver from the at least one other mode to standalone mode.
 17. Thegeolocation system of claim 14, wherein the selective switching of theGPS receiver switches the receiver from standalone mode to the at leastone other mode.
 18. The geolocation system of claim 17, wherein thepredetermined event is a lapse of a predetermined amount of time withoutacquiring at least one GPS satellite signal.
 19. The geolocation systemof claim 14, wherein the wireless communications device can receiveinformation from a second source, the second source selected from agroup comprising a bluetooth network, a Specialized Mobile Radionetwork, a Personal Communication System (PCS) network, a wireless LocalArea Network, an infrared network, a paging network, a two-way pagingnetwork, and an FM broadcast network.
 20. A method for determining thegeolocation of a device, comprising: receiving at least one signal fromat least one GPS satellite at the device, wherein the device can beselectively switched between a standalone mode and at least one othermode; periodically transmitting a frequency reference message to thedevice; and determining the geolocation of the device using the at leastone signal and the frequency reference message.